One of Muammar Gaddafi's closest confidantes, who fled Libya after the revolution, has been sent back from Mauritania, where he sought refuge, to face charges which are likely to include civil rights abuse and mass murder.

As Libya's head of intelligence, Abdullah al-Senussi had been described as the man who knew the innermost secrets of the regime; he had been linked to a number of atrocities both abroad and at home, including the Lockerbie bombing, the murder of WPC Yvonne Fletcher, the blowing up of a French airliner and the slaughter of 1,200 prisoners at the Abu Salim prison in Tripoli.

The delivery of Mr Senussi by the government of Mauritania, after months of negotiations, represents a diplomatic victory for the new administration in Libya. It is, however, another setback for the International Criminal Court (ICC) which had wanted to try him in The Hague for crimes against humanity.

The ICC has also effectively failed in its attempts to get custody of Gaddafi's son Saif al-Islam, who is likely to be tried in the Libyan town of Zintan, where he has been held since his capture last year.

Mr Senussi had been held in Mauritania after arriving six months ago on a flight from Morocco disguised as a Tuareg tribesman. His extradition followed the visit of a delegation led by the Libyan Justice Minister.

Libyan television showed Mr Senussi, heavily bearded and smiling nervously, emerging from a helicopter in Tripoli surrounded by soldiers. Taha Ba'ra, the chief spokesman for the prosecutor general's office in the capital, said: "We received Senussi and he will undergo a number of medical tests. Soon he will also undergo interrogation for the cases he has been charged with and for which he will face trial."

The Mauritanian government, which had previously insisted it would first put the former spy chief on trial over his illegal entry before contemplating claims from other countries, maintained yesterday that it had agreed to the handover after guarantees from the Libyan government that there will be no mistreatment of the prisoner.

The French government has already sentenced Mr Senussi to life imprisonment after a case heard in absentia, involving the shooting down of a UTA airliner over Niger in 1989 in which 170 people were killed. It has also been claimed that he was involved in the destruction of the Pan Am flight over Lockerbie. However, Libya became a staunch ally of the West against Islamists following the rapprochement with Gaddafi led by the US and UK, and Mr Senussi will have details of co-operation which could cause embarrassment on both sides of the Atlantic if aired publicly.

Abdul Hakim Belhaj, a former head of the Libyan Islamic Fighting Group, is currently suing the British Govern-ment and senior officials in this country over his rendition to Libya.

Earlier this year, US House Minority Leader Nancy Pelosi, who led a delegation to the region, said Washington had a "particular interest" in seeing Mr Senussi arrested "because of his role with the Lockerbie bombing".

There are, however, doubts over Libyan culpability in the attack, with strong feeling among many close to the case that Abdelbaset al-Megrahi was wrongly convicted of the bombing.

A trial in Libya will focus on Mr Senussi's part in crushing dissent and the role he played in the Abu Salim massacre when, according to some accounts, he personally ordered guards to open fire on detainees.